diff --git a/native-sql-engine/cpp/src/codegen/arrow_compute/ext/hash_aggregate_kernel.cc b/native-sql-engine/cpp/src/codegen/arrow_compute/ext/hash_aggregate_kernel.cc
index 716b2191c..7aee5540e 100644
--- a/native-sql-engine/cpp/src/codegen/arrow_compute/ext/hash_aggregate_kernel.cc
+++ b/native-sql-engine/cpp/src/codegen/arrow_compute/ext/hash_aggregate_kernel.cc
@@ -906,38 +906,44 @@ class HashAggregateKernel::Impl {
       auto length = in[0]->length();
       std::vector<int> indices;
       indices.resize(length, -1);
-      for (int i = 0; i < length; i++) {
-        auto aggr_key_validity = true;
-        arrow::util::string_view aggr_key;
-        if (aggr_key_unsafe_row) {
+
+      arrow::util::string_view aggr_key;
+      if (aggr_key_unsafe_row) {
+        for (int i = 0; i < length; i++) {
           aggr_key_unsafe_row->reset();
-          int idx = 0;
+
           for (auto payload_arr : payloads) {
             payload_arr->Append(i, &aggr_key_unsafe_row);
           }
           aggr_key = arrow::util::string_view(aggr_key_unsafe_row->data,
                                               aggr_key_unsafe_row->cursor);
-        } else {
-          aggr_key = typed_key_in->GetView(i);
-          aggr_key_validity =
-              typed_key_in->null_count() == 0 ? true : !typed_key_in->IsNull(i);
-        }
-
-        // 3. get key from hash_table
-        int memo_index = 0;
-        if (!aggr_key_validity) {
-          memo_index = aggr_hash_table_->GetOrInsertNull([](int) {}, [](int) {});
-        } else {
+          // FIXME(): all keys are null?
           aggr_hash_table_->GetOrInsert(
-              aggr_key, [](int) {}, [](int) {}, &memo_index);
+              aggr_key, [](int) {}, [](int) {}, &(indices[i]));
         }
+      } else {
+        for (int i = 0; i < length; i++) {
+          if (typed_key_in->null_count() > 0) {
+            aggr_key = typed_key_in->GetView(i);
+            auto aggr_key_validity =
+                typed_key_in->null_count() == 0 ? true : !typed_key_in->IsNull(i);
+
+            if (!aggr_key_validity) {
+              indices[i] = aggr_hash_table_->GetOrInsertNull([](int) {}, [](int) {});
+            } else {
+              aggr_hash_table_->GetOrInsert(
+                  aggr_key, [](int) {}, [](int) {}, &(indices[i]));
+            }
+          } else {
+            aggr_key = typed_key_in->GetView(i);
 
-        if (memo_index > max_group_id_) {
-          max_group_id_ = memo_index;
+            aggr_hash_table_->GetOrInsert(
+                aggr_key, [](int) {}, [](int) {}, &(indices[i]));
+          }
         }
-        indices[i] = memo_index;
       }
 
+      max_group_id_ = aggr_hash_table_->Size() - 1;
       total_out_length_ = max_group_id_ + 1;
       // 4. prepare action func and evaluate
       std::vector<std::function<arrow::Status(int)>> eval_func_list;
diff --git a/native-sql-engine/cpp/src/precompile/hash_map.cc b/native-sql-engine/cpp/src/precompile/hash_map.cc
index 991c36b5c..d55156fc6 100644
--- a/native-sql-engine/cpp/src/precompile/hash_map.cc
+++ b/native-sql-engine/cpp/src/precompile/hash_map.cc
@@ -68,6 +68,7 @@ namespace precompile {
                                        void (*on_not_found)(int32_t)) {                \
     return impl_->GetOrInsertNull(on_found, on_not_found);                             \
   }                                                                                    \
+  int32_t HASHMAPNAME::Size() { return impl_->size(); }                                \
   int32_t HASHMAPNAME::Get(const TYPE& value) { return impl_->Get(value); }            \
   int32_t HASHMAPNAME::GetNull() { return impl_->GetNull(); }
 
diff --git a/native-sql-engine/cpp/src/precompile/hash_map.h b/native-sql-engine/cpp/src/precompile/hash_map.h
index df78033e0..de1613557 100644
--- a/native-sql-engine/cpp/src/precompile/hash_map.h
+++ b/native-sql-engine/cpp/src/precompile/hash_map.h
@@ -28,6 +28,7 @@ namespace precompile {
                               void (*on_not_found)(int32_t), int32_t* out_memo_index); \
     int32_t GetOrInsertNull(void (*on_found)(int32_t), void (*on_not_found)(int32_t)); \
     int32_t Get(const TYPE& value);                                                    \
+        int32_t Size();                                                    \
     int32_t GetNull();                                                                 \
                                                                                        \
    private:                                                                            \